The Diversity-Multiplexing-Delay Tradeoff in MIMO Multihop Networks With ARQ

The authors study the tradeoff between reliability, data rate, and delay for half-duplex MIMO multi-hop networks that utilize the Automatic-Retransmission-reQuest (ARQ) protocol both in the asymptotic high Signal-to-Noise Ratio (SNR) regime and in the finite SNR regime. They propose novel ARQ protocol designs that optimize these tradeoffs. In particular, they first derive the Diversity-Multiplexing-Delay Tradeoff (DMDT) in the high SNR regime, where the delay is caused only by retransmissions. This asymptotic DMDT shows that the performance of an N node network is limited by the weakest three-node sub-network, and the performance of a three-node sub-network is determined by its weakest link, and, hence, the optimal ARQ protocol needs to equalize the performance on each link by allocating ARQ window sizes optimally.